Why don't all rocks have foliation?

Not all rocks exhibit foliation because foliation is primarily a characteristic of metamorphic rocks that have been subjected to directed pressure and temperature, causing minerals to realign into parallel layers. Igneous rocks, which form from the cooling of molten material, and sedimentary rocks, which are formed from the accumulation and lithification of sediments, generally lack this layered structure. Additionally, the specific mineral composition and the conditions of formation play a crucial role in whether foliation develops. Consequently, only certain metamorphic environments and rock types will display foliation.